The effects of antiinflammatory steroids on the response of the guinea-pig isolated ileum to acetylcholine, histamine, nicotine, 5-hydroxytryptamine and electrical stimulation.

High concentrations of antiinflammatory steroids (2.5-40 microgram/ml) reversibly inhibited the electrically induced contractions of the guinea-pig isolated ileum. At 40 microgram/ml they also reversibly inhibited contractions elicited by acetylcholine, histamine nicotine and 5-hydroxytryptamine. PGE1 (2.5 ng/ml), PGE2 (2.5 ng/ml) and PGF 2 alpha (25 ng/ml) antagonized these effects. The inhibition of contractions elicited by direct agonists were less pronounced than those elicited by indirect or partly indirect agonists. The inhibitory effect of steroids may be related to non-specific actions on biological membranes. An overall sensitization of the smooth muscle by PG's may explain their antagonism to inhibition by steroids.